This invention relates to screening apparatus for separating relatively fine material from coarse material and more particularly to a shaker screen assembly for such an apparatus which is able to receive exceptionally heavy materials.
In many separators known in the art, gravel or the like is laid across a vibrating shaker screen. The screen has a mesh size suitable for passing particles of a predetermined size therethrough while supporting and carrying larger particles to a chute, conveyor or the like. As a rule of thumb, it is generally stated that the downwardly sloping length of the shaker screen should be about two and a half times the width of the screen in order to maximize the separating rate and the quality of separation while keeping the separator to a reasonable size. Such separators generally require hoppers at the input end of the shaker screen to funnel the particles onto the screen. One or more output chutes or conveyors are also generally required to carry the separated material away from the shaker screen.
Shaker screens are generally sturdy enough to handle gravel and to separate the gravel from loam and the like. However, large rocks and stumps which would destroy the screens must be separated by a scalper or feeder. The scalper includes heavy bars spaced close enough to feed large rocks to a crusher. Gravel, loam and the like pass through the scalper bars to a conveyor for transfer to the shaker screen.
Rich soil, or loam, is presently high in demand. Due to many regional restrictions on excavating, however, those who supply loam must often go to remote locations that offer rough top soil and separate the loam from coarse material such as rocks, gravel, decaying root stumps and so on. In order to avoid having to transport both the loam and the coarse material, it is highly desirable that a portable apparatus be used for separating the loam from the coarse material. To this end, many past shaker screen separators mounted on a truck or trailer have been reduced-scale imitations of stationary separator plants. Such separators generally require a conveyor or chutes to carry the separated loam and coarse material away from the shaker screen. Also, because of the extended lengths and reduced widths of these shaker screen separators, the separators require infeed hoppers or conveyors. Unless scalpers have been incorporated into the plants, these separators have not been reliable in separating loam from extremely bulky material, such as root stumps and the like, which have clogged the hoppers or conveyors.
In my copending patent application, Ser. No. 947,380, filed Oct. 2, 1978, for a Loan Screening Apparatus, I disclosed a shaker screen apparatus having a generally square shaker screen assembly. That apparatus has been used successfully to receive very bulky, heavy material such as tree stumps to separate that heavy material from finer loam. Except for the width of that screening assembly relative to its length, the screening assembly mounted in that apparatus is conventional. It includes two side plates joined by crossbeams which support upper and lower screens. With continuous use and with heavy loads dropped directly on the screen, heavy bending strains on the crossbeams were noted. Also, because of the extended width of the screens, continued shaking weakened the screens.
An object of the present invention is to provide added strength to a shaker screen assembly to make it better able to withstand extensive loading of heavy materials. A further object of the invention is to provide such a strengthened shaker assembly which does not unduly increase the complexity and weight of the shaker structure.